The terrestrial Judith River Formation of northern Montana was deposited over an approximately 4 Myr interval during the Campanian (Late Cretaceous). Despite having been prospected and collected continuously by palaeontologists for over a century, few relatively complete dinosaur skeletons have been recovered from this unit to date. Here we describe a new genus and species of ankylosaurine dinosaur, Zuulcrurivastator, from the Coal Ridge Member of the Judith River Formation, based on an exceptionally complete and well-preserved skeleton (ROM 75860). This is the first ankylosaurin skeleton known with a complete skull and tail club, and it is the most complete ankylosaurid ever found in North America. The presence of abundant soft tissue preservation across the skeleton, including in situ osteoderms, skin impressions and dark films that probably represent preserved keratin, make this exceptional skeleton an important reference for understanding the evolution of dermal and epidermal structures in this clade. Phylogenetic analysis recovers Zuul as an ankylosaurinankylosaurid within a clade of Dyoplosaurus and Scolosaurus, with Euoplocephalus being more distantly related within Ankylosaurini. The occurrence of Z. crurivastator from the upper Judith River Formation fills a gap in the ankylosaurine stratigraphic and geographical record in North America, and further highlights that Campanian ankylosaurines were undergoing rapid evolution and stratigraphic succession of taxa as observed for Laramidian ceratopsids, hadrosaurids, pachycephalosaurids and tyrannosaurids.

Ethics

ROM 75860 was acquired by the Royal Ontario Museum in June 2016 and is permanently reposited at the ROM. It was legally collected in 2014 from private, deeded land, with landowner permission. Detailed acquisition and locality information are available from the ROM upon request.

Data accessibility

Electronic supplementary material, S1 and S2 are included as supplementary files at Royal Society Open Science. Additional high-resolution photographs of the skull, jaws and tail, and a video of the digital model of the skull and jaws, are available as supplementary materials at Dryad:

V.M.A. and D.C.E. participated in the design of the study, collected the data, participated in data analysis and wrote the manuscript. Both authors gave final approval for publication.

Competing interests

We have no competing interests.

Funding

V.M.A. is funded by a Natural Sciences and Engineering Research Council (NSERC) Postdoctoral Fellowship and a L'Oréal-UNESCO for Women in Science NSERC Postdoctoral Fellowship Supplement. Previous research travel for V.M.A. was funded by an NSERC Canada Graduate Scholarship—Doctoral, an Alberta Ingenuity Studentship, an NSERC Michael Smith Foreign Study Supplement, the University of Alberta China Institute, the Dinosaur Research Institute and the Jurassic Foundation. D.C.E. was supported by a Natural Sciences and Engineering Research Council of Canada Discovery Grant (NSERC grant file number: RGPIN 355845, http://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=527922). Fieldwork associated with this research was supported by the Royal Ontario Museum Reproductions Fund and the Royal Ontario Museum Collections & Research Fieldwork Fund.

Acknowledgements

Acquisition of ROM 75860 was made by possible by the Louise Hawley Stone Charitable Trust at the Royal Ontario Museum. We thank M. Williams and Theropoda Expeditions LLC for the opportunity to acquire the specimen for the ROM. We are grateful to T. Heitkamp for facilitating access to the type locality and for collection data, and C. Morrow and K. Busch for access to the specimen while in their care and for their initial preparation of the specimen. We thank F. Fanti, D. Eberth, M. Ryan, T. Cullen and R. Rogers for discussions regarding the geology of the Havre area. D. Larson and J. Welsh provided advice on the construction of the species epithet. Special thanks are extended to D. Dufault for execution of the figures, and I. Morrison and S. Sugimoto for preparation of the specimen. J. Hulme laser scanned the skull. B. Boyle expertly photographed the specimen. TheropodaExpeditions LLC gave permission to reproduce photographs of the skull in figures 1e and 2d. Thanks also go to K. Seymour, B. Iwama, K. Chiba and M. Mader for logistical support at the ROM. P. May and R. Sissons provided logistical support at Research Casting International. TNT is made freely available with the sponsorship of the Willi Hennig Society. Thanks to reviewers R. Sullivan and P. Dodson and editor K. Padian for constructive comments on earlier drafts of this manuscript.

Published by the Royal Society under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, provided the original author and source are credited.